SOME OBSERVATIONS ON THE VIRUS OF VACCINIA 
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pure, less dilute virus could be obtained. This method of 
repealed partial disinfection might be applied for the puri¬ 
fication of other contaminated viruses. 
We bave also obtained a pure active and multiplying virus 
from incubated tissue préparations. The plasma in wbic-h lhese 
préparations are put up is usually so lytic to ordinary conta- 
minating organisms, that it is only when these are présent in 
great numbers that contaminated préparations are the resuit. 
The lytic action of the plasma makes this tissue method of 
value not alone for vaccinia, but also for the purification of 
other viruses and tissues. 
Combination of virls of vaccinia with living tissue 
cells in vitro (IIarrison’s method). 
Several years ago, Doclor Poor,Doctor Lambert and I applied 
Harrison’s method of growing tissue in vitro to the study of 
the viruses of certain infections in which the spécifie living 
agents hâve not yet been identified or are cultivated with 
difficulty. The three viruses studied thus far with this method 
hâve been those of rahies [5], vaccinia and syphilis [6]. In the 
study of rahies we found that when fragments of brain tissue 
were incubated in blood plasma, inclusions were produced in 
the ganglion cells from normal or rabid brains. These inclu¬ 
sions resembled certain small forms of Negri bodies. There 
was, however, no evidence of a multiplication of the virus, and 
in only a single instance was the virus virulent after 8 days 
incubation at 37°5. Later, Levaditi [7] by employing this 
method found a virus virulent after 30 days incubation. 
After the results with rahies, in conjunclion with Doc- 
tors Israeli and Lambert [8 and 9], Harrison’s method was 
applied to the virus of vaccinia, again with two objects in 
view : — the possible cultivation of the virus outside of the 
body, and the possible production of vaccine bodies in vitro. 
Tecfinie : — Small pièces of rabbit or guinea-pig tissue were placée! for a 
few minutes in a weak émulsion of virus. The pièces were then transferred 
with a small quantity of the virus to cover-glasses to which drops of rabbit 
or guinea-pig blood plasma were added. The cover-slips were immediately 
inverted and sealed over hollow ground slides, which were incubated 
